Alkaline Copper Quaternary or ACQ for short is the latest pressure treatment for lumber for outdoor applications such as decks and retaining walls. ACQ pressure treated lumber was created to remove the arsenic that was an ingredient in the old CCA (Copper, Chromate, Arsenate) pressure treated lumber.
Many studies have indicated that the older style CCA pressure treated lumber was not only an environmental hazard as the arsenic had a tendency to leach into the soil, but it was also a health hazard as the arsenic was entering our bodies when it made contact with our skin.
Metal corrosion with ACQ pressure treated lumber
Of course nothing is perfect and the chemicals that create the new ACQ pressure treated lumber are much more corrosive to metals than the older CCA pressure treated lumber was.
If you are building a deck or any other structure using the new ACQ pressure treated lumber you must pay very close attention to the fasteners that you are using to hold your structure together. If you have a half box of galvanized nails that you used on an older structure utilizing CCA pressure treated lumber they should NOT be used with the new ACQ pressure treated lumber as they will corrode relatively quickly.
The same applies to joist hangers and other metal fittings.
Although there are new nails, joist hangers and other metal fittings specially made for use with ACQ pressure treated lumber, I highly recommend that you use stainless steel nails, joist hangers and other metal fittings. Stainless steel will give you the longest life by far.
ACQ metal fittings and nails are identified on the item as being compliant for use with ACQ pressure treated lumber.
Note: Remember that the same ACQ pressure treated lumber corrosion problems apply to metal items that may be sitting directly on a deck or other structure.
- Egress Windows & Decks
- Deck Board Spacing
- Replacing Deck Boards
- ACQ Pressure Treated Lumber
- Cleaning a Redwood Deck
- Composite Deck Material – Recall!
- Deck Preservation
- Constructing Deck Foundations
- Using Cantilevers In Decks